Teeth generally become more darkly pigmented with age and exposure to materials such as tea and coffee, and it has long been a goal of dentistry to provide a means to safely and effectively reverse this darkening process. Historically there are two approaches to the problem. The first involves removing pigmentation that has adhered onto the surface of the teeth. The conventional techniques commonly use abrasives, sometimes augmented with solvents. While rapidly effective, these techniques have the disadvantage of only being able to remove external stains, leaving all internal pigmentation unchanged. Thus, the whitening effect is extremely limited.
A second technique involves a method of using oxidizing agents to penetrate into the tooth structure and bleach out the undesired pigmentation. The active agents are usually either weak solutions of carbamide peroxide or hydrogen peroxide.
At present, the method of application of the whitening agent utilizes either custom or stock dental trays that are shaped to hold a separate aqueous composition containing the bleaching agent against the teeth to be whitened. The trays are filled with gel or liquid peroxide, and worn for long periods of time, sometimes even overnight. After a series of lengthy treatments, the teeth usually begin to show the desired whitening effect.
While effective on both external and internal discolorations, one major problem encountered with the custom stock dental trays and the aqueous solutions stems from the materials used. All of the aqueous solutions of peroxide ("wet" peroxides) begin to break down and lose effectiveness with time. One particularly useful active agent utilized in such compositions is formed from the combination of water and granular urea peroxide. When granular urea peroxide is isolated from moisture and humidity it has a extremely long shelf life, but once mixed with water it breaks down to urea and hydrogen peroxide and immediately begins to degrade. Although this degradation is desirable while in use--since it is the reaction products that causes the bleaching effect--it is undesirable during shipping and storage. An attempt to overcome this limitation has been made by adding gelling agents such as Carbopol, Pemulan, and the like, to the urea peroxide solution. Although the gels extend the useful life of the peroxide, they also slow down its effectiveness during use. Some products. cannot be shipped during certain times of the year or over weekends as they loose too much potency during the shipping period due to temperature variations. Thus, most of the products currently on the market require use within a short time after manufacture and often require refrigeration during storage.
Another problem of the current moist whitening agents in use is that they cannot be conveniently carried by the customer for fear of leakage from the packaging. Leakage of a bleach material into the surrounding area of a pocketbook, pocket, or briefcase can be disastrous.
In general, the most effective application of conventional whitening agents is by placement in a custom-formed tooth stent or tray. Unfortunately this normally requires an additional visit to the dentist, and will require the patient to endure the tooth impression procedure. In addition, the cost of the extra material and labor can be significant.
Alternatively, some people use the pre-mixed gels in a stock or non-custom tray. Unfortunately the fit of the stock trays to the teeth is imprecise and the bleaching gel rapidly leaks from the tray. It is for this reason that the effectiveness of the stock trays currently in use is limited: after a very short time the bleaching agent will leak out leaving insufficient active ingredient in the tray. In addition to being inefficient, this configuration causes the patient to swallow a much larger amount of bleaching agent than necessary.